Plumbing an Interface

An interface must be plumbed before it can pass
traffic between the system and the network. The plumbing process involves
associating an interface with a device name. Then, streams are set up so that
the interface can be used by the IP protocol. Both physical interfaces and
logical interfaces must be plumbed. Interfaces are plumbed either as part
of the boot sequence or explicitly, with the appropriate syntax of the ifconfig command.

When you configure an interface during installation, the interface is
automatically plumbed. If you decide during installation not to configure
the additional interfaces on the system, those interfaces are not plumbed.